Absorbable wound pad



Jul? 6, 1954- .1.0. Bowz-:R 2,682,872

ABSORBABLE WOUND PAD Filed June 29, .1950

taneous freezing of at least the supericial portion of the mass, and must be continued for a substantial interval to produce the desired result. Using a 3G cc. test tube as the receptacle, and a constant melting point mixture of carbon dioxide and refined kerosene or other hydrocarbon as a standard of reference, I have found that the desired result will be produced in from 2 to 3 minutes. The temperature of such a refrigerant will bein the neighborhood of -70 C. Using the same size test tube and liquid air, at approximately 180 C., the desired result will be produced in from approximately 30 seconds to 1 minute. If larger batches are treated, the time of freezing must be extended.

I prefer to use receptacles containing about 300 cc., and to employ Methyl Cellosolve (monomethyl ether of ethylene glycol) and Dry Ice as the refrigerant, freezing being maintained for 18-24 hours, at well below -70 C. The frozen material is then permitted to thaw. It is then in the state of a solution-that is, it is a clear homogeneous liquid, free of precipitates or sediment or suspended solid matter, even under microscopic examination. This solution may be f referred to as a hemoglobin solution, or as an hemoglobin-electrolyte-stroma solution (abbreviated as H. E. 5.).

The solution produced in accordance with the foregoing technique (which, as previously noted,

is disclosed and claimed in my copending application above referred to) is the material of which the wound pad of the present invention is composed. 'Ihe wound pad itself, in finished form, consists essentially of a porous, relatively frangible, readily absorbable cake of this solution, in a thoroughly desiccated state, enclosed within a glossy envelope or membrane, also formed from the solution, by methods. hereafter described. Toughness, resilience, and an increased resistance to moisture are imparted to this membrane as later pointed out.

One method for producing the wound pad of the present invention from a solution of blood such as just above described is diagrammatically illustrated in the accompanying drawings, and more fully explained hereinafter.

Figure l is a longitudinal section through a two-part ampoule, used in producing the wound u had of this invention.

Figure 2 is a longitudinal section through a refrigerating bath, showing the ampoule of Fig. l partly in elevation and partly broken away.

Figure 3 is a diagrammatic illustration, showing the relative arrangement of the parts during the desiccating step of the process.

Figure 4 illustrates in elevation the inished ampoule, with its two parts separated to expose a portion of the wound pad, the remainder of the pad being still within one part of the ampoule.

Figure 5 is a perspective view of a wound pad at the time of use, showing the normally cylindrical shape attened to adapt it to the contour of the wound.

Figure 1 shows, in assembled relation, the various parts used to form the vessel in which the wound pad of this invention is to be produced. These parts are, primarily, two tubular members, l! and l2, which are united by means of a sealing collar i3, preferably of rather tightlystretched rubber. Considering the member Il, it will be seen that it is of fairly large diameter at the end which abuts the corresponding end of the other tubular member l2, and that this largediameter portion is of substantial length. If, for' example, a wound pad of about 12 cm. long and 1.75 cm. in diameter is to be produced, the largediameter portion of the tube l l will be 2 cm. inside diameter and about 8 cm. in length. At that distance fromy the open end, the tube Il is narrowed, forming the annular shoulder I4, and the narrow tubular neck l5, which has a length of about 4 cm. The short end, l, will have a largediameter portion only about 4 cm. long, but will in all other respects be a counterpart of the member il. Conventional skirt caps I6 are applied to close the ends of the narrow necks. These caps are preferably of the type which has a soft center plug l1, through which a hypodermic needle may be inserted, and which are self-sealing when the needle is withdrawn.

Figure l, as mentioned above, shows the parts in assembled relation. In carrying out my process, the first steps are preferably performed before the parts have been assembled in this way. Considering now these preliminary process steps:

The rst step of the process is to coat the inner surfaces of the members Il and I2 with a fairly substantial lm of the hemoglobin-electrolytestroma solution previously described. This may be done in any convenient manner, as by immersion, spraying, or spreading. I prefer the latter, using a medicine dropper to place the desired amount of solution in the tube and then rotating or manipulating it to assure even distribution of the film over the entire inner surface of at least the large-diameter portion. If dipping is used, it is desirable, immediately after removing the tube from the liquid, to wipe the liquid off the outer surface.

The second step of the process is to subject the film or layer of I-I. E. S. solution, immediately after it is spread, to the action of alcohol. rfhis I prefer to do by immersing the tube in a beaker of alcohol for several minutes, removing it, and permitting it to dry in air. Alternatively, the alcohol also may be applied by spraying or otherwise. If, for any reason, the treatment with a1- cohol is delayed, so that the surface of the coating of H. E. S. solution has begun to dry, contact with alcohol must be prolonged. If so much time elapses before the alcohol is applied that the stratumof H. E. S. solution has completely dried out, the alcohol treatment should be continued for a matter of hours rather than minutes. Under such circumstances, overnight immersion in alcohol is recommended.

It should be mentioned that the thickness of the stratum of solution is important. To check this factor, it is desirable to hold the tube to the light after the stratum has been inundated with alcohol, and visually examine the texture and color of the lm. The color and refraction of the film or coating under transmitted light is a ready and quite reliable index to the thickness, quality, and state of the film. If a thin coat is wanted, the nlm should be almost transparent and light pink in color; if a very heavy coat is needed, the film should. be dark red and almost opaque.

The thickness of the film may be varied by using a more concentrated hemoglobin-electrolyte-stroma solution, by manipulating the tube so as to facilitate run-off or to retard or prevent run-off, etc. If heavier lms than can be provided in these ways are needed, the process may be repeated one or more times, that is, the cylinder may be dipped into the blood solution (or sprayed, or otherwise coated), may be sub- `iected to alcoholic action, and be dried and visually inspected as many times as may 4lbe needed. With very 'little practice it possible to produce and levaluate accurately, precisely the quality of nlm desired.

The action of the alcohol on the Vblood'coating is quite significant. On examination with the vunaided eye, the surface appears glossy, as though varnished Under microscopic examination it seems that the coating has become minutely crystalline in character. Whether or not the Vresioluum of solution adhering to the inner surface of the glass -tube is actually crystalline, the fact is that the material is very much more coherent. 'The deposit which remains seems to have been transformed into a membranous 1inling for the cylinder, rather than a residual deposit.

After the membranous lining has been built up and cured as just described, the outer surface `of each of the tubular members II and I2 is coated -with castor oil or some other semi-drying -or non-'drying oil, for a short distance back Yfrom the end of the large-diameter part. 'The rubber Ycollar I3 is then stretched over one of the largediameter ends; 'the other large-diameter end is brought into endwise abutment, and the rubber Ycollar is slid back across the junction. The Voil facilitates positioning the collar, and also serves to ensure that the joint sealed by the colla-r Will be air-tight. Caps I6 are then applied, and the vessel is `now ready for the next step in the process. 'This is the -condition illustrated in Fig- ;gure 1, the mem-branous lining being indicated at I3'.

An alternative procedure `for carrying out these "Y preliminary steps is to brin-g the tube ends together and apply the Vcollar I3 before spreading the H. E. S. Vsolution over the inner surface.

L If this is done, the solution is injectedy as by use of 'a long-needle syringe, through neck Iinto the rlarge-dianleter space, and is .spread by manipulation. This is not as 'desirable7 however, because air-drying of the 'film after inundation with alcohol seems to be quite important, and it 'takes undesirably long to circulate a suflicient volume of air Athrough the narrow necks I5.

The next step in the process is the formation of .a hollow cylinder of H. E. Si. solution within 'the ampoule A. The apparatus used in carrying out this step is illustrated in Figure 2. It

consists of a vessel I9 having upper Wall surfaces I'Qa, lled almost to the brim with refrigerant 28. This refrigerant may be a vmixture of Dry Ice and refined kerosene, or any other intensely cold liquid such as Methyl Cellosolve (melting point A large size hypoderrnic syringe 2I is used to inject the H. E. S; solution through the cap I6 and neck I5 into the large-diameter portion of the ampoule. I prefer Vto use an instrument having .a barrel about 3 cm. in diameter and about l2 cm. long, provided with an extra-long needle 22, of 18 or 20 gage for preference. The "7" (18 cm.) size is long enough for most purposes.

'The .syringe is charged with H. E. S'. solution rthe lampoule A is 'continually rotated, spit-Wise,

so that the solution deposited on the inside of the membranous 4layer I8 is spread evenly over the surface and is progressively frozen in a thin lay-er. The needle tip 23 is traversed several times, back and forth through the Wide-diameter section, care being taken to maintain substantially constant pressure on the plunger so as to ensure a Vuniform rate of discharge ci the solution. Rotation of the ampoule is 'laintained al1 the while, so that a Abody 2A of frozen solution is gradually huilt up, from the periphery towards the center of the ampoule. Each fresh increment of solution -ireezes to the layer of solution Vpreviously injected and frozen.

. When the body or" frozen material reaches such a thickness, radially, as to leave a central, axiallyeytending core space 25 of about 0.5 cm. in diameter, the needle is Withdrawn and the ampoule is connected to a desiccation unit, as show-n diagrammatically in Figure 3. In the present eX- ample, when the volume of the ampoule is about 40 ce., the amount of liquid injected is from 30-35 ycc. In an'eiiort to expedite building up of the body of frozen material, I have simply :dlled the ampoule about four-fifths full oi H. E. S. solution before placing it in l'the refrigerant; have then immersed it in the refrigerant and rotated it quite rapidly during freezing. seful results can be secured in this way, if rotation is mai-ntain-ed at a speed'suihcient to drive all o1 the liquid tothe periphery by centriiugal force and keep it pad ultimately produced is likely to he distinctly more fra-ngi leV than when the Vsolution is frozen sequentially in layers during relatively much slower rotation. f

In any case, when the desired body ci frozen material has been provided, the cap It is removed from one end of the cylinder and the vacuum line from a conventional lyophiliaing unit is substituted. Mechanism or" this sort is now Well known in this art, and it is therefore only ldia- -gramniatically illustrated in Figure It coinprises a test tube for biological liquid to be desiccated (or several such tubes connected to a common manifold), a vacuum line 2li to a primary condenser 2'?, through ywhich vapor withdrawn from the material being treated, and a vacuum pump 2d. In the present case the an poule A is substituted for the usual test tube, and the `vacLu-irn yconnection is made oy removing one lof the caps i@ and substituting a ported nipple, as illustrated at 25% in Figure 3. In the primary condens r "2l, the larger part of the moisture content of the material in the ampoule A collected `in the form of vapor and precipitated in the form of ice. One or more secondary condensers '30 may he used if desired.

For reasons not yet clear to nie, when the lmaterial being desiccated is a. blood solution incorporating the disintegrated residue or" blood corpuscle-s, such as the hemoglobin-electrolytestroma solution referred to heretofore, it seems to be much more important to maintain the temperature at a low value, and to maintain the degree vacuum applied at a high value than when lyophilizing plasma. Otherwise, the material lin the cylinder lI-l' tends to reliquefy, and iiow to the bottom oi the cylinder, so that channel is no longer available in the body of material through which vapor may be withdrawn. If its level reaches that ci the exhaust port, the liquid may completely rplug this passage and refreeze there.

- lne ya general indication, I may vsay 'that bestresuits have been secured when the vacuum gage showed from to 15 microns, throughout the process of desiccation, and the thermometer showed temperatures around 70 C`. or, better still, 90 C. at least until a. major portion of the free moisture had been sublimated.

If the frozen mass does re-liquefy, the ampoule must be removed and its contents must be refrozen, spinning the ampoule quite rapidly to displace the liquid and re-establish the axial cavity while freezing takes place. As suggested above, the pad ultimately produced When this is clone is more frangible than when the solution is sequentially frozen.

I surmise that the problem is consequent upon the presence of all of the electrolytes normally present in the blood, since under my process nothing is removed of the useful blood constituents, except, permissively, that quantum of plasma which is deemed unnecessary, and which is I separated by centrifugal action before the blood residue is initially frozen. Certainly the freezing point of the hemoglobin-electrolyte-stroma solution which I use is much lower than the freezing point of plasma.

Preferably, the lyophilizing treatment is carried on until practically all free moisture has been removed. Using a small size commercial lyophilizing unit, having a 24-position manifold, I continue desiccation for from 18` to 24 hours. according to the manufacturers manual, should ensure that not more than 1% of the moisture content initially present will remain.

I have discovered that the membranous lining which was first produced Within the ampoule tends to adhere to the blood solution injected and frozen in situ as previously described, and tends to `separate from the glass Wall of the cylinder when the material in the cylinder shrinks in volume as the Water is removed. Indeed, some degree of separation is initiated by the alcohol treatment, and one indication that that treatment has progressed sufficiently is the appearance of indications that the film or coating is no longer firmly adherent. As the volume of the mass being desiccated is reduced, the membrane thus becomes a jacket or shell for the contents of the ampoule. Ultimately, there Will be an annular cake of desiccated blood residue Within the cylinder, encased Within the cured H. E. S. membrane. It is therefore possible to remove the entire charge as a cohesive, handleable unit. It may then be pressed into the desired shape, placed in a hermetically-sealed container, and stored until used.

In practice, I much prefer to avoid the extra handling involved in removing the desiccated Wound pad, shaping it, and 1re-packaging it, for reasons both of economy and sterility. Instead, after desiccation has been finished, I prefer to seal the ends of the ampoule in which the Wound pad was formed, so that this same ampoule becomes the package in which the wound pad is stored and sold. This may be done by removing the ported nipple 29 to which the vacuum line had been connected, and replacing the rubber cap I6.

A better procedure, in my opinion, is to nameseal both ends of the wide-diameter section while it is still under vacuum. A short section of flexible tube 32 is inserted in the vacuum line for this purpose. When desiccation is complete, this exible tube is clamped shut, and is removed from the vacuum line While still attached to the ampoule by the short tube 33 and the ported nipple This, 2

29. Then the necks l5 are flame-sealed adjacent the shoulders i4, producing a pig-tail closure, most clearly seen in Figure 4, where the reference character 3l identifies it.

At the time of use, the surgeon breaks the seal (as in Figure 4) by freeing the collar I3 from the long end Il of the ampoule. The short end i2 of the ampoule is then Withdrawn, leaving the short end of the Wound pad 24 projecting from the region of the break. This is usually done in the surgical pavilion at the time of an operation. When the short end of the ampoule has been cornpletely removed, the surgeon, Wearing sterile gloves, grasps the Wound pad by the short end, and slides the entire pad bodily out of its container. The Wound pad may then be applied to the injury. If it seems desirable rst to modify its shape or general dimensions, so as to iit the contour of an incision, it is only necessary to press it manually into the shape desired. The membranous envelope is sufficiently strong to avoid crumbling or breaking of the desiccated material Within it.

It should be pointed out that the membranous envelope just referred to, and described in detail in an earlier section of this specification, performs several quite important functions. In the first place, it facilitates separation of the Wound pad from the cylinder Wall during desiccation. In its absence, the solution adheres to the cylinder Wall irregularly--so that as the annular cake shrinks during desiccation, it adheres in some places and pulls away in others, fracturing into relatively large chunks in so doing. In the second place, the membrane serves as a jacket for the pad, lending tensile strength and also helping to corinne any desiccated material which may be present in free particle form after the pad has been removed from the cylinder. It would be difiicult to press the Wound pad into special shapes without crumbling it or breaking it, if the membrane were not present. Also, I believe that, under vacuum, separation of the membrane from the cylinder wall facilitates desiccation, by permitting withdrawal of Vapor from the periphery as well as from the center of the pad.

But over and beyond these important functions, the membrane serves a very significant purpose in the use of the pad during healing. This is a most interesting aspect of the present invention. Subjecting the solution applied to the cylinder wall to the action of alcohol imparts to the membrane a certain degree of resistance to dissolution. Upon the addition of Water, the desiccated residue of an H. E. S. solution is dissolved, in the absence of this membrane, in a matter of seconds, or at the most, minutes. Wherever there is an injury in living tissue, the adjacent areas will be suffused with blood, which is predominantly aqueous. If it were not for the water-resistive characteristics of the membranous envelope, the substance of the wound pad might be hydrated too quickly.

It is possible to increase or diminish the degree of resistance to absorption simply by regulating, iirst, the thickness of the membranous envelope referred to, and second, the length of time for which it is exposed to the action of alcohol. Thus it is possible to coat the inside of the cylinder rather lightly, immersing it in alcohol for a relatively brief interval, and thus produce a jacket for the Wound pad which will dissolve, comparatively speaking, in a very short time. This is desirable, particularly where a superficial injury is to be dressed, because the material Within the` membranous envelope possesses evenl ing cells which they seem to be capable of absorbing directly. Where the wound pad is used in this way, it is desirable that the membranous envelope should retain its resistance to the solubilizingreect of bodily fluids for a longer interval, so that the substance of the Wound pad will not be quickly hydrated and carried away from the wound, but will be gradually absorbed, right at the site of the injury.

Where the incision is a deep one, as in abdominal surgery, absorption should proceed still more slowly, so that the substancerof the wound pad may be'kept in place, to exert a maximum of its beneficial healing action over the longest possible interval of time.

It is my belief that hospitals and surgeons will nd it desirable to keep on hand at least three grades of wound pads made according to this process, one grade being absorbable quite shortly after application; another persisting long enough for tissue to recuperate sufliciently to permit ambulation of many post-operative patients, and the third having a life expectancy of many days or possibly even weeks.

The foregoing comments illustrate a preferred embodiment ofmy invention. Variation of procedure may be employed, within limits, without departing from the spirit. This is especially true of the manipulativesteps, which are presently performed mainlyY by hand, but which seem to be readily adaptableY to mechanical operation. I contemplate several modifications along. this line, such as the use of power-rotated quick-acting chucks, to seize and spin thel ampoules; of automatic traverse mechanism to control the injection of I-l. E. S. solution during freezing; and oi metering injectors to secure controlled discharge of a predetermined quantum of iiuid. Unitary ampoules could be used with such equipment, especially if an air injector were employed to facilitate drying after the alcohol treatment, in which case a fracture line would be inscribed in place oi the collar I3.

Physiological alterations are also possible. One such adaptation which I have used-is to incorporate glucose in the hemoglobin-electrolyte-stroma solution employed to form the membranous envelope. I find that additions in the neighborhood of 8% of glucose may be used to advantage, where the presence of glucose is indicated.

The alcohol which I prefer to use is medicinal alcohol, preferably ethyl alcohol. This may be obtained at various concentrations, as is well known. It is desirable to utilize relatively concentrated forms-say 75% CzI-IsOH, and upwards, although it is by no means necessary to use absolute alcohol. If solutions of lower concentration than 75% alcohol are used, some of the I-I. S. lm may difuseinto the liquid when the cylinder is dipped therein, and, if glucose is present, somey oi it wil-l do likewise. Moreover, the toughening or curing action is influenced by the degree of concentration of pure alcohol presv mitted to remain there.

10 ent. The more dilute the alcohol solution, the longer it takes to cure the membrane.

Although ethyl alcohol is preferred, isopropyl alcohol, one of its homologues, may also be used. It toughens the film and imparts resistance to absorption, but tentative conclusions are that clinical eiiectiveness may be somewhat reduced when it has been'employed. Mixtures predominantly of ethyl alcohol and containing relatively minor amounts of iso-propyl alcohol yield results which compare favorably with those secured vwith ethyl alcohol alone.

It is also possible to incorporate certain drugs, medicines, or biologicals in the hemoglobin-electrolyte-stroma solution before desicoation, or to place them in the hollow core of the wound pad after desiccation. Such additions, however, should be selected with care, so as to ensure compatibility, both as to chemical composition and as to biological eiect, with the hemoglobinelectrolyte-stroma constituent. My Patent No. 2,477,171 describes and claims the combination of an hemoglobin-electrolyte-stroma solution with penicillin. Such a solution may be utilized in forming the wound pad of the present invention, with very satisfactory results, where the employment of an antibiotic is indicated. Streptomycin .is similar in eiect. Delayed action medication is possible, by placing a desired medicament, in dry form, or, in small quantities, in liquid form, or even in capsules, in the hollow core of the wound pad. Preferably, this is done at the time of use, and the ends of the wound pad are squeezed together thereafter, so that much of the wound pad will have to be absorbed beforethe capsule is dissolved or the medicament is released. v

In summary, it will be seen that a newsurgical instrumentality of considerable utility has been created. Since it contains all of the. constituents of blood and no reaction products hostile to blood, it is as much 'at home in living tissue as if it had been whole blood administered yby transfusion.

VTet it is, I think, more useful than transfused blood, for it can be utilized without limitation as to therblood `type Gr.RH factor'Y of either the patient or of the vf griginal donor. lFurthermore, the stroma, being in a state of submicroscopic disintegration, is apparently in a form which makes itdirectly available to living cells, without assimilative action being needed Yelsewhere in the body. It; is more useful than plasma, for it contains not only the life-giving hemoglobin but also the tissue-building stroma, not Vto mention the blood electrolytes. Furthermore, it is not carried more or less at random to the site of the injury- (as with intravenous injections), but'is applied precisely at the pointof need, where much of it is directly used, and from which some of it is dilfused, with beneficial effect upon surrounding tissue. To these advantages must be added the eiectiveness of th-e wound pad in curtailing loss of body iiuids-its hemostatic actionits capacity to absorb fluids which are released, and its capacity to be absorbed gradually, so that it may quite safely be embedded in living tissue and per- The potential usesv of this wound pad as a medium for applying other l therapeutics are also wide indeed.

size and shape herein described, if 3 cc. of H. E. S.

solution is employed to form the lining nlm or coating, and exposure to alcohol is continued for l minutes, the film will be light pink in color and will be quite translucent. The wound pad will resist absorption for almost two days if applied to a superiicial injury. If the amount of solution used to form the lm is doubled (application in two stages is recommended under such circumstances) and exposure to alcohol is also doubled, the film is deeper in color and transmits noticeably less light. A wound pad encased in such a membrane will not be completely absorbed at the end of five days When applied to a superficial injury, but will be absorbed within that time if implanted in the abdominal cavity. Using 9 cc. of blood solution, in three applications of 3 cc. each, with minutes of exposure to alcohol after each application, a lm will be produced which is deep red in color and only slightly translucent. A wound pad having a membranous covering of this character, implanted in the abdominal cavity, may resist complete absorption for ten days or more.

Numerous departures from the comparative illustrations given just above have been made, and all tend to confirm the view that careful control of the amount of solution used and time of alcohol treatment can be relied upon to produce a predetermined absorption time with considerable accuracy. As a general rule, exposure to alcohol should be continued for a longer time where a thick film is applied in a single stage than Where a lm of the same thickness is applied in two stages. Thus, in the third example given above, if 9 cc. were applied in a single stage, the alcohol treatment would have to be continued for almost an hour, instead of thirty minutes.

I claim:

1. A surgical wound pad comprising a porous body of desiccated organic material absorbable in tissue fluids, having adhered to at least a major portion of its outer surface a relatively non-porous coat comprising the same organic material but in a state less readily absorbable in tissue uids than said body.

2. A surgical wound pad as defined in claim 1, having a centrally disposed cavity therein.

3. A surgical wound pad as dened in claim 2, wherein the porous body is composed entirely of constituents of animal blood.

4. A surgical wound pad as defined in claim 1 having its porous body composed of constituents, including at least hemoglobin, of animal blood.

5. A surgical wound pad as defined in claim l, in which the non-porous coat comprises the product which results from exposing to alcohol a solution of red blood constituents.

6. A surgical wound pad having an inner body and membranous material adhered to at least the major outer surface areas of said body, char-` acterized in that it is composed primarily of the desiccated residues of the corpuscular portion of animal blood, both in its inner and in its outer portions.

7. A surgical wound pad as defined in claim 6 characterized in that it is completely absorbable in tissue fiuids.

8. A surgical wound pad as dened in claim 7, in which the inner body is porous and hydroscopic and the membranous material is relatively non-porous, and relatively resistant to hydration.

9. A surgical wound pad as defined in claim 7, in which the membranous material comprises the product which results from applying alcohol 12 to a film of blood solution and evaporating said alcohol in the presence of air.

10. A process for producing a surgical wound pad, which process comprises the steps of distributing a solution containing the corpuscular constituents of blood over the inner surface of a sterile vessel to form a lm, applying alcohol to the film so formed, evaporating the alcohol in air, and forming a body of dry therapeutic material within said film.

11. A process according to claim l0, in which the body of therapeutic material comprises the corpuscular constituents of animal blood.

12. A process according to claim 1l, in which the corpuscular constituents of animal blood are introduced within the confines of the lm in a fluid state and are subsequently desiccated.

13. A process for producing a surgical wound pad, which process comprises the steps of distributing a solution containing the corpuscular constituents of blood over the inner surface of a tubular glass vessel to form a tubular film, treating the film so formed with alcohol and evaporating the alcohol to transform the nlm into a tubular membrane, innlling the membrane with a tubular annulus of frozen material comprising the corpuscular constituents of animal blood by spraying such constituents in fluid form radially outwardly from the tubular axis while applying refrigeration at temperatures of the order of C.; and then desiccating the material so frozen by sublimation under vacuum in the frozen state.

14. A process according to claim 13 which includes the step of flame-sealing the glass vessel while still under vacuum.

l5. In the process of desiccating animal uid in the frozen state by vaccum, the steps which consist in chilling the space within a tubular vessel by application of a refrigerant to the outer surface of said vessel, introducing the animal. fluid axially of said vessel, and spraying it generally radially outwardly towards the inner periphery of said vessel whereby to distribute said uid as an annular lni within said vessel, the process being characterized in that the rate of spraying and the temperature of the refrigerant are so correlated as to produce extremely rapid freezing of said film, and being further characterized in that introduction of fluid is continued, forming annular lms which freeze to the annular lm previously formed, until a substantial. body of frozen material having an axially disposed channel therethrough has been provided.

16. The process of claim l5 in which the tubular vessel is partially immersed in the refrigerant and is subjected to rotation about its major axis during spraying and freezing of said fluid.

17. The process of claim 15, in which the film is formed by axial traverse of nozzle means.

18. The process of claim i6 in which the film is formed by axial traverse of nozzle means.

19. The process for producing a wound pad having hemostatic properties, which process comprises the steps of introducing a preparation containing red blood cells in the state of a solution into a vessel producing a film of such solution by distributing it over the inner surface of said vessel; applying alcohol to the film, and evaporating the alcohol in the presence of air, whereby to transform the lm into a cured membrane; introducing a quantity of the solution first mentioned within the membrane; distributing said solution in a layer within said membrane and freezing said layer immediately after its 13 formation; repeating said introduction, distribution, and freezing steps until a substantial body of frozen material has been built up, but leaving an axially extending vapor channel through said body of frozen material; and thereafter desiccatingr the frozen material by the sublimation of its Water content in vacuo.

20. The process of claim 19, in which desiccation is carried out at temperatures at least as cold as -'70 C.

21. Apparatus for producing a wound pad comprising a tubular vessel provided with tubular trunnions at either end,k a refrigerant chamber having means for supporting said trunnions with the vessel in a horizontal position, pump means for injecting an animal fluid under pressure into said vessel, and a hollow retractable conduit member extending from said pump means into Said vessel through one of said tubular trunnions, and having spray nozzle means at least adjacent its delivery end.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date Y 779,338 Williams Jan. 3, 1905 2,254,915 Sawyer Sept. 2, 1941 2,310,082 Holbrooke Feb. 2, 1943 2,380,823 Brown July 31, 1945 2,448,153 Reid Aug. 31, 1948 2,492,458 Berling, Jr Dec. 27, 1949 2,518,123 Y Chavanon Aug. 8, 1950 2,533,004 Ferry et al. Dec. 5, 1950 FOREIGN PATENTS Number Country Date 865,377 France Feb. 24, 1941 

1. A SURGICAL WOUND PAD COMPRISING A PROOUS BODY OF DESICCATED ORGANIC MATERIAL ABSORBABLE IN TISSUE FLUIDS, HAVING ADHERED TO AT LEAST A MAJOR PORTION OF ITS OUTER SURFACE A RELATIVELY NON-POROUS COAT COMPRISING THE SAME ORGANIC MATERIAL BUT IN A STATE LESS READILY ABSORBABLE IN TISSUE FLUIDS THAN SAID BODY. 